quick question - anyone got a rear light bulb 12v21/5W hanging around and a multimeter? could you measure the resistance through each filament for me and let me know what it is.
Thanks
SKidMark

Not my field of expertise, but, I have a reading of , less than .2 of an OHM on one, and virtually zero on the other.
I cleaned the terminals before measuring.
I don't have a spare holder to test which is which though.
Mike

I don't have a lamp in front of me to measure, but should be able to work it out with basic forumlae.

P = IV, so I = P/V = 21/12 = 1.75A for 21W filament.
and 5/12 = 0.417A for 5W filament.

Then, V = IR, so R = V/I = 12/1.75 = 6.86 ohm for 21W filament
and 12/0.417 = 28.78 ohm for 5W filament.

Hope that helps

thanks for your reply guys. Hallsy I already calculated that but I used R-E2P as they were the values I had...
Anyway the calculated values and measured values don't tie up as Mike's figures showed. The reason for all this was to figure out which wire at the Tail/Brake light was for each. I know that the green is GND but could someone tell me which of the brown and green/yellow are for the tail light and which is for the brake light.

Cheers SkidMark

I take the capacitor out of the wiring system (the one near the headstock) and replace it with a lower voltage battery (I use a PP9 (9v)). This way I can test all the wiring and switches.

You could use a much lower voltage if you think that 9v would damage the electronics I suppose but this is the way I've always done it without problems. Can't get much current to do damage due to the internal resistance of such a small battery .

But ARs are such finicky creatures ...........

thanks but just tried that doesn't seem to work on a AR - I got the neutral light on but nothing else...

Check the colour of the wires coming out of the brake light switch .

knackeredMk1 wrote:Check the colour of the wires coming out of the brake light switch .

THANK YOU - black and green/yellow so I can take it that the green/yellow is the feed for the brake light!